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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 05-15-2011
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Bonding/Electrolysis

So we hauled Laurie Anne last week for bottom paint, zincs, and some paint touch up. Everything looked pretty good until I noticed some rust on the strut around where the strut is welded to the pipe that houses the cutlass bearing. There is a lot of electrolysis and after grinding the soft stuff out it appears that someone that shall remain nameless (PO) covered it up with some kind of filler, and he also didn't bother bonding it to the hull zincs. Of course this would have required a 2.5' piece of wire and crimping two eyes to the ends so I can understand why he didn't do it . Hopefully it will be able to be welded, otherwise I will need to have a new piece made and then welded to the strut in exactly the same location so that the prop shaft will line up. I feel kind of stupid because I didn't check that the strut was bonded, but in my defense the bolts are directly under the engine oil pan and you have to be upside down and know where to look to even see them. Just a heads up to check that all of your stainless is bonded to your zincs, I don't even want to know how much having a new one of these might cost.



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Old 05-15-2011
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Sheesh John - that's not pretty, is it? Not sure if I've ever seen a SS strut before. Is it possible that it was welded with the wrong rod and that's part of the problem?

Are you hoping to try to fix this without pulling the shaft? Obviously the cutlass will have to come out first...
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Old 05-15-2011
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Stainless Strut? Like Faster, I did not know that they existed...

What kind of boat is it?

My O'day has a bronze strut, not attached to the bonding system either.
Here is a pic;


The shaft is a 1" bronze shaft. The prop has a 1¼" id, and there is a nylon bushing between the shaft and the prop, thus electrically isolating the two. The prop has NO issue with corrosion, despite evidence elsewhere that the boat had galvanic corrosion issues.

Were your boat mine, I would be looking to replace the entire strut.
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Old 05-15-2011
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The boat is a 1988 Brewer Three Seas 40. The entire strut, including the custom cast part that matches the hull is stainless. The cutlass carrier was welded on, and as you can see, the corrosion is just to the side of the weld. I don't have anyway of knowing what type of rod was used but for some reason that is where the electrolysis chose to attack (in my experience that is also where welds usually break). Two SS welders that I had look at it have seen this before (apparently SS struts are common on large power boats), immediately said it must not be grounded and they were right.
Replacing the whole strut and having a custom bronze one cast sounds like it might be a little expensive so I'm hoping it can be welded (after grinding it out with a die grinder it actually cleaned up really well and looks like solid SS to weld to). I'm keeping my fingers crossed.
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Old 05-16-2011
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Your diver should've alerted you to that issue. You're lucky you didn't lose the strut.
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Old 05-16-2011
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That would be me Fstbttms (no commercial dive services on our island). I dive it once a year to replace the zincs and scrub the parts of the hull that the long brush doesn't reach. The PO had filled the crevice with some kind of filler so it wasn't until it was hauled that we could see the rust stains and investigate.
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Old 05-16-2011
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Quote:
Originally Posted by jrd22 View Post
The PO had filled the crevice with some kind of filler...
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